1. Field of the Invention
The present invention relates to a transmission for use in a power transmitting system for transmitting the power of an internal combustion engine mounted on a vehicle such as a motorcycle to a wheel of the vehicle. More particularly, the present invention is addressed to a constant-mesh transmission for a vehicle to which the rotation of a crankshaft of the internal combustion engine is transmitted through a clutch.
2. Background Art
A conventional constant-mesh transmission for use in a power transmitting system for transmitting the power of an internal combustion engine mounted on a motorcycle to a wheel of the motorcycle is described in Japanese Patent Laid-open No. 10-159973. Such a conventional constant-mesh transmission is shown in FIG. 9 of this application. Referring to FIG. 9, reference character a denotes a constant-mesh transmission, in which the rotation of a crankshaft 6 of an internal combustion engine is transmitted through a multiple-disc friction clutch c to a main shaft d as an output rotating shaft of the clutch c, and further transmitted through a plurality of constantly meshing transmission gears e and f to a counter shaft g. The rotation of the counter shaft g is transmitted to the wheel through a chain wrapped around a sprocket h fixed to one end of the counter shaft g.
In more detail, a transmission gear is mounted on one of the main shaft d and the counter shaft g so as to be non-rotatable relative thereto, and another transmission gear constantly meshing with the above relatively non-rotatable transmission gear is rotatably mounted on the other of the main shaft d and the counter shaft g. In shifting the transmission gears, a shifting mechanism n including a gear shift pedal (not shown), a gear shift arm i, shift pins j, a shift drum k, and gear shift forks m is operated to thereby axially move a shifter splined with the other shaft toward the rotatable transmission gear on the other shaft. As a result, a projection (referred to as xe2x80x9cdowelxe2x80x9d) formed on the shifter comes into engagement with a recess or hole formed in the rotatable transmission gear on the other shaft, so that the rotatable transmission gear on the other shaft is integrated with the other shaft. Accordingly, the counter shaft g is rotated relative to the main shaft d at a speed determined by a gear ratio between the transmission gears.
In such a constant-mesh transmission, the rotating speed of the shifter is different from the rotating speed of the transmission gear to be engaged with the shifter, so that the engagement of these two members accompanies impact, causing a shift shock and an impact noise.
In starting the vehicle from a rest condition, the transmission is in a neutral position and the clutch is in an engaged condition, so that the main shaft is kept in rotation by the torque of the crankshaft and the counter shaft is not in rotation. To start the vehicle from this condition, the clutch is once disengaged and the shifting mechanism is operated to shift the transmission from the neutral position to a first-speed position. At this time, although the clutch is in the disengaged condition, the main shaft is kept in rotation by inertia. Accordingly, when the shifter comes into engagement with the transmission gear, a large shift shock and impact noise may occur because of a relatively large difference in rotating speed between the shifter and the transmission gear.
It is accordingly an object of the present invention to reduce a shift shock and an impact noise upon shifting in a constant-mesh transmission for a vehicle.
In accordance with the present invention, there is provided in a constant-mesh transmission for a vehicle including first and second rotating shafts rotatable by the torque transmitted through a clutch, a first transmission gear rotatably mounted on the first rotating shaft, and a second transmission gear constantly meshing with the first transmission gear and mounted on the second rotating shaft so as to be non-rotatable relative to the second rotating shaft. A resisting member is provided between a rotational portion of the first rotating shaft and the first transmission gear for imparting a rotation resisting force to the first rotating shaft or the first transmission gear.
With this configuration, when the transmission is in a neutral position, the first rotating shaft (or the second rotating shaft) is kept in rotation by the torque transmitted through the clutch in its engaged condition. The rotating speed of the first transmission gear (including its non-rotative condition) is different from that of the first rotating shaft, because the first transmission gear is rotatably mounted on the first rotating shaft and constantly meshes with the second transmission gear mounted on the second rotating shaft so as to be non-rotatable relative thereto.
When the clutch is disengaged to carry out gear shifting from the above condition, the first rotating shaft or the first transmission gear receives a rotation resisting force from the resisting member, because the first rotating shaft (or the second rotating shaft) keeps rotation by inertia and the resisting member is provided between the rotational portion of the first rotating shaft and the first transmission gear both rotating at different speeds. Accordingly, a difference in rotating speed between the first rotating shaft and the second rotating shaft rotating integrally with the first transmission gear through the second transmission gear can be reduced. As a result, the impact upon engagement of the shifter and the transmission gear can be reduced to thereby reduce a shift shock and an impact noise.
In starting the vehicle from a rest condition, the first rotating shaft is kept in rotation by the torque of the crankshaft through the clutch, and the second rotating shaft is not in rotation, for example. When the clutch is disengaged in this condition, the first rotating shaft receives a rotation resisting force from the resisting member provided between the rotational portion of the first rotating shaft and the first transmission gear not rotating, so that the rotating speed of the first rotating shaft is reduced. As a result, the impact upon engagement of the shifter and the transmission gear can be reduced to thereby reduce a shift shock and an impact noise.
The second transmission gear is mounted on the second rotating shaft so as to be slidable in the axial direction of the second rotating shaft and to be non-rotatable relative to the second rotating shaft, and thereby serves also as a shifter. With this configuration, the number of parts can be reduced and the transmission can be made compact.
The resisting member is an annular member comprising a metal ring and a lip, the metal ring being fixed to the rotational portion of the first rotating shaft or to the first transmission gear. With this configuration, the resisting member can be firmly fixed through its metal ring, and a larger rotation resisting force can be imparted by utilizing a force generated by deformation of the lip.
The resisting member may be accommodated in a recess formed on the inner circumference of the first transmission gear. With this configuration, the resisting member can be accommodated in the recessed space formed on the first transmission gear, so that the resisting member can be compactly accommodated and the transmission can accordingly be made compact.
The resisting member may also be press-fitted with the outer circumference of the rotational portion of the first rotating shaft. With this configuration, structural modification of the transmission can be minimized, and the number of parts can be reduced. Further, the structure can be simplified and the resisting member can be easily mounted.
The resisting member can impart the rotation resisting force to the outer circumference of the rotational portion of the first rotating shaft in an area for mounting the first transmission gear or to the inner circumference of the first transmission gear. With this configuration, the resisting member can be mounted within the mounting area of the first transmission gear on the rotational portion of the first rotating shaft, thereby allowing compact arrangement of the resisting member.
Incidentally, the wording of xe2x80x9crotational portion of a rotating shaftxe2x80x9d used in this specification means a rotational portion of the rotating shaft itself or a rotational portion of a member mounted on the rotating shaft so as to be non-rotatable relative thereto and accordingly rotating integrally with the rotating shaft.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.